Name: iridium
Symbol: Ir
Atomic number: 77
Atomic weight: 192.217 (3)
Group in periodic table: 9
Group name: Precious metal
Period in periodic table: 6
Block in periodic table: d-block
CAS registry ID: 7439-88-5
The name iridium is appropriate, for its salts are highly coloured. Iridium is white, similar to platinum, but with a slight yellowish cast. It is very hard and brittle, making it very hard to machine, form, or work. It is the most corrosion resistant metal known, and was used in making the standard metre bar of Paris, which is a 90% platinum-10% iridium alloy. This metre bar has since been replaced as a fundamental unit of length (see Krypton).
Iridium is not attacked by any of the acids nor by aqua regia, but is attacked by molten salts, such as NaCl and NaCN.